Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Designing of an enclosure for RF power amplifier (RFPA) requires adequate knowledge of electromagnetic field distribution inside the housing. Enclosure design for a high power RF device or appliance is very important as it not only provides mechanical or structural support, but also acts as a suitable path for heat transfer, causing thermal relief, protection against hostile environments such as temperature, humidity, vibration/shock, electromagnetic interference (EMI)/electromagnetic compatibility (EMC) etc.
RFPA with very high power and gain requires multiple stages of amplification. This multistage amplification combined with Doherty configuration increases the size of the RFPA. Resonance mode exists in a cavity if largest cavity dimension in enclosure of the RFPA is greater than or equal to one half of free space wavelength. Conductive surface of enclosure supports several resonant modes, and therefore produces oscillating charges, which in turn induce surface currents on conductive trace of the PCB. Cavity resonance of a high power RF amplifier Enclosure not only degrades electrical performance but can also cause unwanted oscillation in frequency band of interest because of feedback through the resonance mode. Resonance caused inside the enclosure coupled with RFPA device (even in a quiescent state) may even result in catastrophic failure of the device due to peak oscillating voltage exceeding the device′ breakdown voltage.
There have been efforts in the art to dampen resonance by suitable placement of RF absorbers, as discussed by P. Dixon in his research titled “Cavity resonance dampening”; J. Dhar, R. K. Arora in their research titled “Enclosure effect on microwave power amplifier”; and Deepak Ghogaonkar, Sanjeev Gupta and Ashish Sarvaiya in their research titled “Interaction of Active MMIC with Package/Housing”. To have more attenuation at low frequency, for example around 1-2 GHz, RF absorber has to be cascaded, which increases enclosure height of the power amplifier. Thermal conductivities of RF absorbers are bad, i.e. around 0.2 W/m k, as stated by L. Meyer, S. Jayaram, E. A. Cherney in their research paper titled “Thermal conductivity of filled silicone rubber and its relationship to erosion resistance in the inclined plane test”. Therefore, RF absorber blocks the heat radiation through it which in turn increases the temperature of the cavity. To compensate for such increase in temperature, extra cooling mechanism for high power amplifier may be required. Due to the foretold temperature and height issue, the RF absorber is not a good choice.
Another alternative was proposed by D. F. Williams in there search titled “Damping of the resonant modes of a rectangular metal package”. This research states that resonant cavity modes can be damped by placing a dielectric substrate coated with a resistive film in the cavity. By using dielectric substance coated with resistive film, Q factor can be reduced to some extent. U.S. Pat. No. 5,030,935 proposes dampening of unwanted resonant modes in an enclosure for microwave circuitry carried on a conductive ground plane by interrupting the ground plane at one or more locations about microwave circuitry. However, the proposed arrangement is not suitable in case of high density circuit.
Therefore, there is a need in the art for providing a method for resonance mitigation in RF high power amplifier enclosure, and also for an enclosure for RF high power amplifier that is designed to mitigate resonance.
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about”. Accordingly, in some embodiments, numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that, the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.